Black nail holes and seams

Q: I just had new red oak floors installed. They were stained with a natural stain, and then the first coat of water-based urethane applied. When the floors were dry and we inspected them, we noticed an area where the nail holes have bled black, and the end seams are black as well.

What causes this, and what is the fix? Does the entire floor need to be re-sanded?

A: Not sure about the end seams but the nail holes are water and steel. Such holes should be filled first before applying a water borne finish. All things said and done, this is a very difficult job, and what may happen on one site does not always happen on another. If the job as a whole seems good, perhaps you can look at this as an isolated incident. If your particular floor has a high mineral content, that may explain the dark end boards. I cannot even imagine anything a sanding company could do that would be the cause of such a thing, so it is peculiar to your floor.